Radiotelephones including cellular telephones and cordless telephones are ubiquitously used for day-to-day communications. Such radiotelephones utilize various frequency bands to transmit signals. For example, cellular telephones transmit signals in the 824 to 849 MHz band pursuant to the advanced mobile phone system (AMPS) cellular standard. With the licensing of additional spectrum for personal communications system (PCS) use, the cellular telephones can also transmit signals in the 1.85 to 1.91 GHz PCS band. On the other hand, handsets of cordless telephones may transmit signals at a frequency band of 2475 MHz to 2483.5 MHz, which is within the FCC provisions for unlicensed, non-spread-spectrum, industrial, scientific, medical (ISM) band use.
Radiotelephones capable of transmitting signals over multiple frequency bands are well-known. One such radiotelephone is disclosed in U.S. Pat. No. 5,406,615 issued to Miller, II et al. The disclosed radiotelephone is a handset capable of communicating signals over the cellular band and the ISM band. The circuits of the multi-band radiotelephones including the Miller handset are more or less duplicative of those of single-band radiotelephones. As such, with respect to a single-band radiotelephone, a multi-band radiotelephone is normally more bulky in size, costly and unreliable as the manifold circuit components are introduced into the radiotelephone. For example, among other things, the multi-band radiotelephone typically employs in a transmitter a power amplifier for each of the many transmit frequency bands. Such a power amplifier is usually expensive and bulky.
Accordingly, there exists a need to improve the circuit of a multi-band communications system, in particular, the multi-band radiotelephone, so that the circuit utilizes the space more efficiently, and is less expensive and more reliable.